This invention relates to the field of signal validation. In particular, this invention is drawn to a system for validating quadrature signals generated by sensors in a steering control system.
In control systems, it is common to use sensors to generate signals relating to various conditions in the system. The sensor signals can then used by the control system in any desired way. For example, in a steering control system, various conditions are sensed (e.g., wheel speed, motor speed, steering wheel speed and position, etc.) and used by the steering control system. It is therefore important that signals generated by sensors are accurate in order to describe what is occurring in the system.
It is also common to use sensors that generate quadrature signal pairs. For a valid quadrature pair, both signals should have nearly a 50% duty cycle and be nearly 90 degrees out of phase. These characteristics ensure that a microprocessor in a control system will have enough time to decode the signals, and to provide correct measurement of speed and direction of a sensed object.
One problem with sensors that generate quadrature signals is that the quadrature signals may not meet the desired duty cycle and phase requirements. This may be due to several factors. For example, the sensor may be misaligned, causing the duty cycle of the signals to be much greater or much less than 50%. Misalignment may also cause the signals to be more or less than 90 degrees out of phase. Also, the sensor itself may fail, or may not be capable of producing quadrature under all conditions. For example, some sensors produce correct quadrature only when the object they are sensing is rotating at a particular speed. Also, propagation delays from electronic circuitry may alter the phase relationship of the signals.
It can therefore be seen that in order to have confidence that a control system is functioning properly, quadrature signals should be evaluated for accuracy and validity.
A method of validating a quadrature signal pair from a sensor in a steering control system is provided, including the steps of: detecting consecutive voltage transitions in first and second signals of the quadrature pair; for three consecutive detected voltage transitions, calculating the elapsed time between the first and second voltage transitions and the elapsed time between the second and third voltage transitions; and determining the validity of the quadrature signal pair by comparing the calculated elapsed times.
Another embodiment of the invention provides a method of validating a quadrature signal pair in a steering control system comprising the steps of: detecting when a first signal of the quadrature pair changes states; detecting when a second signal of the quadrature pair changes states; and evaluating the validity of the quadrature signal pair based on when the first and second signals change states.
Another embodiment of the invention provides a steering control system comprising: a quadrature sensor for sensing conditions in the system and generating a quadrature signal pair; a processor coupled to the quadrature sensor, wherein the processor performs the following functions: detecting edges in first and second signals of the quadrature pair, after detecting a plurality of consecutive edges, calculating elapsed time periods between consecutive edges, and determining the validity of the quadrature pair by comparing two adjacent elapsed time periods.
Another embodiment of the invention provides a method of validating a quadrature signal pair generated by a quadrature sensor in a control system comprising the steps of: detecting state changes in first and second quadrature signals; calculating the time periods between consecutive detected state changes; and making a determination of the validity of the quadrature signal pair based upon the calculated time periods.